Electrolysis of sugars



gain" Patented Nov. 24, 1942 ELECTROLYSIS or SUGARS Ralph A. Hales, Tamaqua, Pa., assignor to Atlas Powder Company, Wilmington, Deb, a corporation of Delaware Drawing.

Application October 20, 1939,

Serial No. 300,375

(Cl. 204-7'l) 10 Claims.

The present invention relates to improvements in a process for the electrolysis of sugars.

The invention is broadly concerned with an improvement in the electrolytic process for reducingreducible sugars such as glucose and the like in accordance with the teachings of the patent to Creighton'No. 1,990,582. In this process an electrolytic diaphragm cell is employed in which the cathode compartment is separated by a permeable diaphragm from the anode compartment. This patent teaches the use of an amalgamated lead cathode for use in the cell. The catholyte which is in contact with the oath: ode is an aqueous solution of the sugar to be reduced and a suitable electrolyte. r The electrolyte is preferably an alkali metal salt such as sodium sulfate although other alkali metal salts can be used'provided that the anions are not injurious to the reduction or to the cell equipment. The anolyte comprises an aqueous solution of an acid or other suitable electrolyte and is in contact with an anode which is formed of chemical lead or other suitable material.

It has been noted that withamalgamated lead cathodes in the case of reductions in which the catholyte is maintained in a condition of low alkalinity, for example under 10 g. NaOH per literof catholyte or its equivalent, very poor rates of reduction and poor current efiiciency are obtained as compared with reduction at a similar cathode at high alkalinity. Similarly poor rates of reduction are noted with amalgamated lead cathodes where the catholyte is maintained in a weakly acid condition, such as 0.5 to 1.5 g. H2804 per liter of catholyte. The explanation of this phenomenon" is unknown at the present time but amalgamated lead cathodes has entailed considerable loss of time and current efficiency in low alkalinity reductions. For many purposes low alkalinity reductions are desirable and this disadvantage just described makes this type of reduction needlessly expensive as. compared to the high alkalinity reductions. When the rate of reduction and the current efiiciency thereof fall,

there is not only the factor of loss of electric power but also the output of a given group of cell equipment is curtailed.

The present invention has therefore for its object the improvement of the process for the electrolysis of sugars at low catholyte alkalinity or low acidity and with amalgamated lead cathodes.

It has been discovered that the addition of small amounts, for example 0.1 to l0.0 or preferably 2.0 to 4.0 g. per liter of catholyte, of zinc sulfate, speeds up the reduction at low alkalinity or low acidity with a lead cathode anducuts the reduction time substantially in half. The current efiiciencyis correspondingly improved.

a The addition of zinc sulfate to a catholyte appears to be of value principally at low alkalinity, that is, not substantially more than the equivalent of 10 g. NaOH per liter of catholyte and preferably from 0.1 to 2.0 g. NaOH per liter of catholyte, and with amalgamated lead cathodes. At higher alkalinities the lead cathodes have the property of reducing with good efliclency without the aid of the Zinc sulfate and therefore little advantage is gained by using it. It has been noted that an amalgamated lead cathode which has'been used in a reduction in which zinc sulfate was incorporated into the catholyte retains a higher efficiency for reduction at *low alkalinity in thenext succeeding several runs even though no further zinc sulfate is added in the subsequent runs. The invention also contemplates employing this effect and adding zinc sulfate to the catholytes, for example in alternate runs, or the addition of very small quantities of zinc sulfate in each run.

The invention will be better understood from the following examples which compare with the results obtained in practising the invention with results obtained otherwise. The invention is not limited tothe details of the examples nor is it restricted to the electrolysis of glucose but is also applicable to the electrolysis of other reducible sugars such as inverted cane sugar, fructose, mannose, lactose and the like.

In the tables which follow, the data are listed under abbreviated headings which refer to the following:

Con." is the initial concentration of sugar in the catholyte in grams per liter and unless otherwise noted will refer to the concentration of glucose.

Alk." is the'alkalinity of the catholyte in grams NaOH per liter.

Ratio is the quotient of the area of the oathode in square decimeters divided by the number of liters of catholyte. r a

C. D. is the current density in amperes per I square decimeter of cathode area.

T. is the temperature of the catholyte in degrees Fahrenheit.

% s. R. is the time in hours after the start of the reduction at which. 90% of the'sugar is reduced.

99% S. R." is the time in hours after the start of the reduction at which 99% of the sugar is reduced. i

served in two reductions more than the cathode in Example 1 and the reduction time and current efiiciency of Example 2 are therefore better than those of Example 1.

A very good rate of reduction and current efllciency are found in Example 3 where zinc sulfate was added in the proportion of 4 g./l. of catholyte instead of 2 g./l. as in the other three examples.

For the sake of comparison the following examples illustrate reductions comparable in all respects to the. reductions of Examples 1 to 4 except that no zinc sulfate was included in the catholyte.

Table 2 Ex. Conc. an. Ratio 0.1). '1. fie ZnSO P. N. 0.10.

dex of its crystallizing: tendency from-relatively highly concentrated aqueous solutions. The

higher the pyridine number the greater the crys- I tallizing tendency. The greater the complexity of the sorbitol-containing product the less its crystallizing tendency and vice versa.

C. E. is the current efllciency up to 99% sugar reduced corrected for-the yield of polyhydric alcohol.

In each of the following examples the catholyte was an aqueous solution containing 325 g. of glucose per liter and '75 g. of.sodium sulfate per The effect of the zinc sulfate addition is clearly brought out by a comparison of these two tables. Example 5 is a normal low alkalinity reduction at a, fairly new amalgamated lead cathode. It took 258 hours to reduce 99% of the sugar and a current efiiciency of only 17.8% was obtained. Compare Example 1 in which a similar cathode was used but 2 g./l. of zinc sulfate were added. In Example 1 only 165 hours were required to reduce 99% of the sugar and the current efficiency was 27.5%. Thus, the addition of zinc sulfate gave a high rate of reduction even in a run, employing a fairly new, hence relatively inefficient. cathode. Example 2 shows an even better run in which 133 hours were required to reduce 99% of the sugar and the current efficiency was 34.6%.

In Example 3 where 4 g./l. of zinc sulfate were added a further improvement was noted in that only 124 hours were required to reduce 99% of the sugar and a current efficiency of 36.5% was had. Example 6"used an old amalgamated lead cathode and relatively better results were had than with Example 5. Example 4 used. an old than in any of the others. Runs 1 and 2 further serve to show the effect of different cathodes since Example 2 used the same cathode as Example 1 but represents its performance two runs later.

liter. The anolyte atthe start was an aqueous cathode comparable'to that of Example 6 and the solution of 300 g. per liter of sulfuric acid. The current efficiency was 39.9% as against 24.3% anode was 10 lb. chemical lead plates and anode where no zinc sulfate was employed.

area was 8.1 square decimeters. The cathode area The quantity of zinc sulfate that will be used was 9.0 square decimeters. The diaphragm was in a given reduction is subject tp considerable of porous alundum. The alkalinity indicated in variation. Usually it will be desired to use the the examples was maintained by the addition of least possible amount which will give eflicient imsuitable quantities of alkali or acid from time to provement inrate of reduction and current emtime during the reduction. ciency. Therefore, certain of the following Table 1 Ex. Conc. Alk. Ratio (3. D. 'r. 9% ZnSO; P.N. 0.1

1 325 0.5-1.5 2.0 1.0 08 00 105 2g./l. I 72.5 27.5

a 325 0.5-1.5 2.0 1.0 as ,7 124 4g./l. 70.0 30.5

4 325 0.5-1.5 2.0 1.0 00 y 73 113 ZgJl. I 70.0 30.0

The above examples illustrate typical reducclaims refer to a small but efflcient quantity of tions at low alkalinity and with amalgamated zinc sulfate by which is meant a quantity suflead cathodes. The variations in the time of reficient to produce a substantial improvement in duction, current efiiciency and P. N. are traceable the rate f reduction compared to the rate in to a considerable extent to individual differences an otherwise Similar reduction from which the o 1 in the cathodes. FOT Instance, Example 4 used zinc sulfate is omitted. In general. however, it a much older cathode than any of the other excan be Said that refer b] Zi If t amples and the efficiency was higher in this run p a y no su a 6 15 added to the catholyte as from 0.1 g/l. to 10.0 g./l. to obtain the desired improvement. While the examples show the use of the hydrate ZnSO4-7H2O it will be understood that this is only a conven- In other words. the cathode of Example 2 had 7 ient form in which to use the salt and that any other means for introducing a zinc sulfate into the catholyte is to be considered the equivalent.

The invention is not limited to the details of the examples but is limited only by the scope of the following claims.

I claim:

1. A process for the production of polyhydric alcohols in an electrolytic cell having an anode and a cathode respectively in anode and cathode compartments separated by a permeable diaphragm, said cathode comprising amalgamated lead; which comprises maintaining in the cathode compartment and in contact with said cathode an aqueous solution of a reducible sugar, an alkali metal salt as electrolyte, and a small but sufficient quantity of zinc sulfate to increase substantially the rate of reduction of the sugar; and passing an electric current between said anode and cathode and through said sugar solution to reduce said sugar to polyhydric alcohol.

2. A process for the production of polyhydric alcohols in an electrolytic cell having an anode and a cathode respectively in anode and cathode compartments separated by a permeable diaphragm, said cathode comprising amalgamated lead; which comprises maintaining in the cathode compartment and in contact with said cathode an aqueous solution of a reducible sugar, an alkali metal salt as electrolyte, a quantity of an alkali equivalent to not more than grams sodium hydroxide per liter of solution, and from 0.1 to 10 grams of zinc sulfate per liter of solution; and passing an electric current between said anode and cathode and through said sugar solution to reduce said sugar to polyhydric alcohol.

3. A process for the production of polyhydric alcohols in an electrolytic cell having an anode and a cathode respectively in anode and cathode compartments separated by a permeable diaphragm, said cathode comprising amalgamated lead: which comprises maintaining in the cathode compartment and in contact with said cathode an aqueous solution of glucose, an alkali metal salt as electrolyte, from 0.1 to 2.0 grams of alkali per liter of solution, and from about 2 to 4 grams of zinc sulfate per liter of solution; and passing an electric current between said anode and cathode and through said glucose solution to reduce said glucose to polyhydric alcohol.

4. A process for the production of polyhydric alcohols in an electrolytic cell having an anode and a cathode respectively in anode and cathode compartments separated by a permeable diaphragm, said cathode comprising amalgamated lead: which comprises maintaining in the cathode compartment and in contact with said cathode an aqueous solution of glucose, an alkali metal sulfate as electrolyte, from 0.1 to 2.0 grams of alkali per liter of solution, and from about 2 to 4 grams of zinc sulfate per liter of solution; and passing an electric currest between said anode and cathode and through said glucose solution to reduce said glucose to polyhydric alcohol.

5. A process for the production of polyhydric alcohols in an electrolytic cell having an anode and a cathode respectively in anode and cathode compartments separated by a permeable diaphragm, said cathode comprising amalgamated lead: which comprises maintaining in the cathode compartment and in contact with said cathode an aqueous solution of a reducible sugar, an alkali metal salt as electrolyte, from 0.1 to 2.0 grams alkali per liter of solution, and from 0.1 to 10 grams of zinc sulfate per liter of solution; and passing an electric current between said anode and cathode and through said sugar solution to reduce said sugar to polyhydric alcohol.

6. A process for the production of polyhydrlc alcohols in an electrolytic cell having an anode and a cathode respectively in anode and cathode compartments separated by a permeable diaphragm, said cathode comprising amalgamated lead: which comprises maintaining in the oathode compartment and in contact with said cathode an aqueous solution of glucose, an alkali metal salt as electrolyte, from 0.1 to 2.0 grams alkali per liter of solution, and from 0.1 to 10 grams of zinc sulfate per liter of solution; and passing an electric current between said anode and cathode and through said glucose solution to reduce said glucose to polyhydric alcohol.

7. A process for the production of polybydric alcohols in an electrolytic cell having an anode and a cathode respectively in anode and cathode compartments separated by a permeable diaphragm, said cathode 'mprising amalgamated lead: which comprises in intaining in the cathode compartment and in contact with said cathode an aqueous solution of a reducible sugar, an alkali metal salt as electrolyte, a small quantity of an acid, and from about 2 to 4 grams of 'zinc sulfate per liter of solution; and passing an electric current between said anode and cathode and through said sugar solution to reduce said sugar to polyhydric alcohol.

8. A process for the production of polyhydric alcohols in an electrolytic cell having an anode and a cathode respectively in anode and cathode compartments separated by a permeable diaphragm, said cathode comprising amalgamated lead: which comprises maintaining in the cathode compartment and in contact with said cathode an aqueous solution of glucose, an alkali metal salt as electrolyte, a small quantity of an acid, and from 0.1 to 10 grams of zinc sulfate per liter of solution; and passing an electric current between said anode and cathode and through said glucose solution to reduce said glucose to polyhydric alcohol.

9. A process for the production of polyhydrlc alcohols in an electrolytic cell having an anode and a cathode respectively in anode and cathode compartments separated by a permeable diaphragm, said cathode comprising amalgamated lead: which comprises maintaining in the cathode compartment and in contact with said cathode an aqueous solution of a reducible sugar, an alkali metal salt as electrolyte, and from 0.1 to 10 grams of zinc sulfate per liter of solution; passing an electric current between said cathode and anode and through said sugar solution to reduce said sugar to polyhydric alcohol; and thereafter employing said cathode in a subsequent reduction of a reducible sugar in an aqueous solution with an alkali metal salt as electrolyte but without the addition of zinc sulfate.

10. A process for the production of polyhydric alcohols in an electrolytic cell haying an anode and a cathode respectively in anode and cathode compartments separated by a permeable diaphragm, said cathode comprising amalgamated lead: which comprises maintaining in the cathode compartment and in contact with said cathode an aqueous solution of a reducible sugar, an alkali metal salt as electrolyte, and from about 2 to 4 grams of zinc sulfate per liter of solution; and passing an electric current between said anode and cathode and through said sugar solution to reduce said sugar to polyhydric alcohol.

RALPH A. HALES.

CERTIFICATE OF CORRECTION. Patent No. 2,505,210.v I November 2h, 19b2,

RALPH A. HALES.

It is herehy certified that error appears in the printed specification of the above nurhbered patent requiring correction es follows Page 1 first colunin, 1111656, after "but" insert --the fact has been observed and the use of--; and second column, line 26, after "compare" strike out "with";

line 57, for Con."-read --Cono.-; and that the said Letters Patent should be read with this correction therein that the same may conform to the rec- 0rd of the case in the Patent Office.

Signeden'd sealed this 9th day of February, D. 19 4.5.

. Henry Van Arsdale, (Seal) 1 Acting Commissioner of Patente. 

